The former first lady, who as recently as Tuesday declared herself the strongest candidate, gave Obama an unqualified endorsement and pivoted from her role as determined foe to absolute ally.
"The way to continue our fight now to accomplish the goals for which we stand is to take our energy, our passion, our energy and do all we can to help elect Barack Obama, the next president of the United States," she said in a speech before cheering supporters packed into the ornate National Building Museum, not far from the White House she longed to reign in.
"Today as I suspend my campaign, I congratulate him on the victory he has won and the extraordinary campaign he has won. I endorse him and throw my full support behind him and I ask of you to join me in working as hard for Barack Obama as you have for me," the New York senator said.
With that, Clinton placed herself solidly behind her Senate colleague from Illinois, a political sensation and the first black to secure a presidential nomination.
For Clinton and her supporters, it was a poignant moment, the end of an extraordinary run that began with an air of inevitability and certain victory. About 18 million people voted for her; it was the closest a woman has come to capturing a nomination.
Joining her on stage were her husband, the former president, and their daughter, Chelsea, before she took their leave as she addressed the crowd.
Obama secured the 2,118 delegates needed to clinch the nomination Tuesday after primaries in South Dakota and Montana. He planned to spend the weekend at home in Chicago.
Clinton supporters began lining up at dawn to attend the farewell address. A smattering of Obama backers showed up as well, saying they did so as a gesture of party unity.